Hitherto, polyurethane resins have been used in a wide variety of forms including flexible or rigid foams, adhesives, fibers such as spandex, thermoplastic or thermosetting elastomers, and or paints.
They are prepared mainly by the reaction of an organic diisocyanate compound with polyol compounds, particularly the polyurethanes having linear molecular structures are prepared by the reaction of an organic diisocyanate with a long chain having hydroxyl groups in terminal positions, and so-called chain extenders having 2 active hydrogen atoms which have a relatively lower molecular weight.
Specific chain extenders include diols, diamines and or alkanolamines, etc.
The long chain polyol compounds having hydroxyl groups in terminal positions include polyester polyols, polyether polyols such as polypropylene glycols, polytetramethylene glycols, polyols having carbonate groups in their molecular structures, that is, polycarbonatediols, etc.
The specific polyester polyols include polyols which are derived from divalent carboxylic acids such as adipic acid and polyhydric alcohols such as ethylene glycol, 1,4-butyleneglycol and or 1,6-hexanediol, etc., and polylactone polyols which are obtained with .epsilon.-caprolactones, etc., as starting materials.
The specific polyether polyols include polymers of ethyleneoxide or propyleneoxide, copolymers thereof, and or polytetramethyleneglycol which is a polymer of tetrahydrofuran.
Polyurethane resins derived from polyether polyols are used in fields of elastic fibers or urethane elastomers in which low permanent compressive deformation is required.
The specific polycarbonatediols mainly include those having 1,6-hexanediol structures in the molecule.
However, the polyurethanes derived from adipic acid and polyhydric alcohols such as ethylene glycol, etc., have a disadvantage because of a lack of water resistance in spite of the advantage of the elastic recovery property.
On the other hand, the polyurethanes derived from adipic acid and polyhydric alcohols such as 1,4-butylene have a disadvantage because of a lack of the elastic recovery property in spite of the advantage of the water resistance property.
Furthermore, polyurethanes derived from poly-.epsilon.-caprolactone polyols have advantages not only of excellent water resistance property, but also excellent outdoor durability and excellent heat resistance which are disadvantages in the polyether polyols.
However, hydrolysis resistance is not sufficient in the polyurethanes derived from the poly-.epsilon.-caprolactone polyols.
The polycarbonatediols derived from 1,6-hexanediol are usually solid.
Accordingly, it is required that polyvalent alcohols having side chains or polyether polyols having appropriate molecular weight be introduced in order to make them liquid.
As a result of an intensive investigation, the inventor of this invention has now found that it is possible to solve the problems of known polyurethane resins and has prepared polyurethanes having excellent hydrolysis durability by using polyols obtained by copolymerizing .epsilon.-caprolactone with trimethylcaprolactone.